Why green roofs?
Green roofs – designing
The rapid development of cities leads to limitation of the availability of land for the construction of parks and green squares. No wonder that people increasingly want a contact with nature, greenery and the values of nature, also at the expense of conveniences that urban agglomerations create for them. Therefore, for a long time architects, green designers and urban planners have been looking for solutions that would improve the environment, making it more friendly for a human.
It was a great idea to introduce vegetation to empty surfaces: walls and roofs of buildings which resulted, among others, in the development of green roof systems. This brings a whole lot of benefits:
Green roofs help to make urban climate milder, especially in case when it is drastically different from climate of the surrounding areas. Walls and roofs of buildings show heat retention properties. This phenomenon is referred to as “urban heat island”. It means that in centers of big agglomerations, the temperature of air rises by approximately 1- 2°C degrees. Sometimes it can even rise by 10°C. At the same time, humidity drops. Therefore, vegetation on green roofs is necessary because it plays an important role in creating something that can be called an “air pillow”. This process takes place because water cumulated in plants evaporates and the sunlight is reflected from their surface. “Air pillow” therefore, means higher humidity and lower temperature. For instance, a roof covered with bituminous mass, in summer heats even up to 60-70°C, and a green roof, on the other hand, only up to 25-40°C. These numbers speak for themselves. Additionally, only 2 centimeters of green layer can retain up to 60% of rainwater. Later, rainwater evaporates so humidity rises. Moreover, green roofs facilitate operation of urban wastewater system. They increase production of oxygen and reduce amount of CO2 in the air. It is extremely interesting that during one year, a green roof with an area of 15 m2 is capable of producing oxygen for as many as 10 people, and at the same time to absorb 10 – 20% of pollutants and gases from air.
Green roofs reduce traffic noise, thanks to reflecting and partially absorbing approx. 20 – 30 dB.
Green roofs enable giving space an architectonic shape. Moreover, they create opportunity to hide installation equipment on the roofs. They enable creation of homogenous designs thanks to mixing plants in different parts of a building– starting from indoor plants, plants on terraces or roofs to end with plants on the area surrounding the building. Unique compositions make the property stand out.
Green areas can be regained. As a result, full use of a small lots in city centers is possible without interference in urban master planning.
Green roofs offer an additional protection and thermal isolation of the roof. Roof covering is protected from external damage, such as: damage caused by fowl, by wind and sunlight.
It is worth mentioning here the opinion of one of the greatest architects of the twentieth century – Le Corbusier. He called the roof the fifth facade. He claimed that the roof garden would be a favourite place for residents where they would be eager to stay. At the same time, the city will be able to reclaim the entire lost area designated for development. In his opinion, the roof gardens is a perfect opportunity to bring a man from a big city closer to nature. Therefore, he placed this motive at the first place of his programme of modern architecture.
In modern times, where there are more and more new factories, offices, shops, houses and car parks, the words and message of this man gain a unique expression. Aiming at creation of new green areas becomes a priority.
Green roofs are garden-landscape works where vegetation is laid on a special insulating layer without a contact with the soil. Planning and implementation of such an undertaking is a complex operation. Attention must be paid to the differentiated criteria and specific conditions of the case. Most of all, climatic and weather factors, construction and vegetation must be taken into account. At the planning stage, it is also necessary to consider certain transformations of vegetation. They can be minimised by appropriate choice of layers and regular maintenance.
Throughout the year, green roof undergoes natural scheme of vegetation, in accordance with seasonal changes. During dry periods, plants lose their vitality, and during more humid periods, the grow. One thing should be bore in mind, in case of extensive vegetation, plans adjust to the local ecosystem only after a few years.
The main purpose of roof vegetation is to bring forward economic, technical, visual and ecological improvements. The final effect influences not only a single building, but also a whole surrounding area. It is a way to create new green spots in urban areas, which if properly maintained, can be used in other ways.
Green roofs play their proper function in an effective and in a long-lasting way, only if the plants are properly managed and all the technical equipment is regularly serviced. Minimal maintenance requires regular control and clearance of drains, removal of roots of unnecessary plants and debris.
In case of green roofs, there are three types of vegetation. The classification depends on the way of use, technical conditions and type of construction. Each type requires various types of plants and different maintenance. In practice there are three types:
- intensive vegetation
- semi-intensive vegetation
- extensive vegetation